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Similarities of negative absolute temperature to dark energy?

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  1. Jan 6, 2013 #1
    “The inverted Boltzmann distribution is the hallmark of negative absolute temperature; and this is what we have achieved,” says Ulrich Schneider. “Yet the gas is not colder than zero kelvin, but hotter,” as the physicist explains: “It is even hotter than at any positive temperature – the temperature scale simply does not end at infinity, but jumps to negative values instead.”
    1.Does it imply that we can break the stable coherent state of an atom and render it motionless. What does it say about +- excited state of an atom. 2. How about the condition of our universe. Any thoughts?

    http://www.quantum-munich.de/filead...re/Negative_absolute_Temperatur-EN-3.1.13.pdf
    http://www.sciencedaily.com/releases/2013/01/130104143516.htm
     
    Last edited by a moderator: Jan 7, 2013
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  3. Jan 6, 2013 #2

    mfb

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    What do you mean with "motionless"? Cool a gas until most atoms are in the ground state? That is possible, and the result is a Bose-Einstein-condensate.
    Remove everything which could be considered kinetic energy? That is not possible.

    I don't see any relation.
    And I don't see the relation to dark energy.
     
  4. Jan 7, 2013 #3
    I'm not a physicist. Just an avid reader. It's a bit misleading sometimes when they mention of 'At zero Kelvin (-
    460°F or -273°C) the particles stop moving and all disorder disappears. Thus, nothing
    can be colder than absolute zero on the Kelvin scale.'

    From what i know and read; atom is not totally motionless i.e particles position and momentum are not dependent of each other(HUP doesn't allow it). When they mention stop moving, do all particles in the system be completely at rest in their positions means that they will have a definite position and a definite momentum (ie zero)? Which is highly unlikely.

    They always mention dark energy resembling the same effect(thermodynamic behavior of negative temperature) each time i've read that subject on the net. "the atoms in the gas do not repel each other as in a usual gas, but instead interact attractively. This means that the atoms exert a negative instead of a positive pressure. As a consequence, the atom cloud wants to contract and should really collapse – just as would be expected for the universe under the effect of gravity. But because of its negative temperature this does not happen. The gas is saved from collapse just like the universe."
     
  5. Jan 7, 2013 #4

    mfb

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    0K (as coldest temperature) corresponds to everything in its ground state. Due to quantum mechanics (related to the uncertainty principle), the energy is above the ground state we would have in classical mechanics. This difference can be interpreted as potential and kinetic energy - even if the system is perfectly static, so the wave function (describing the particle) does not move.

    Dark energy is not a gas.
     
  6. Jan 7, 2013 #5

    Chalnoth

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    When you have a very special sort of quantum system that has a maximum possible energy, then and only then can you have negative temperatures.

    This comes about because if you have a maximum possible energy, then the entropy of that state necessarily has very low entropy. And systems tend to avoid low-entropy configurations. How do you increase the entropy of a maximum-energy state? You reduce its energy. So the moment you bring this system into contact with some other system that is at a normal temperature, it loses energy to the other system, no matter what the temperature of this other system is.

    This means a few things:
    1. The idea of cooling an object below absolute zero is nonsense: temperatures below absolute zero are hotter than any positive temperature.
    2. You also can't heat an object to negative temperatures: anything you use to try to heat it will only be at some positive temperature. This means that you have to sort of "trick" the system, for example by changing the energy states available so that what was a positive-temperature state becomes a negative temperature state.
    3. Negative temperature states generally won't last very long: you can't keep them completely out of contact with other matter, so they will tend to lose energy quite rapidly until they come into equilibrium with their surroundings. But they may, in some cases, last long enough to be measured.
     
  7. Jan 7, 2013 #6
    ... Neither did we know 'if' it has any or so 'physical property' (signs maybe 'assuming a dark energy as fluid having jeans mass) to it(limited to methodology of effects). In some sense both resembles the same effect or the best, the closest we have as a physical effect. If you want to put it that way. Bit far fetch but Interesting nonetheless.
     
  8. Jan 7, 2013 #7
    Oh.. Now it makes more sense. Thanks for pointing out some of my missing info's!
     
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